Pollution control devices are employed on motor vehicles to control atmospheric pollution. Such devices include catalytic converters and diesel particulate filters or traps. These devices include a pollution control element. For example, catalytic converters typically contain a ceramic or metal monolithic structure that supports the catalyst. The catalyst oxidizes carbon monoxide and hydrocarbons, and reduces the oxides of nitrogen in engine exhaust gases to control atmospheric pollution. In addition, diesel particulate filters or traps typically contain a wall flow filter in the form of a honeycombed monolithic structure, usually made from porous crystalline ceramic materials. Each of these devices has a metal housing (typically stainless steel) which holds or mounts the pollution control element. Such pollution control elements are typically fragile and susceptible to vibration or shock damage and breakage. The damaging forces may come from rough handling or dropping during engine assembly, from engine vibration or from travel over rough roads.
Such pollution control elements are also typically subject to damage due to high thermal shock, such as from contact with road spray. To protect the pollution control element, especially the ceramic monolithic type, and to prevent exhaust gases from passing between the pollution control element and the surrounding housing (thereby bypassing the catalyst or filter), mounting mats are disposed between the pollution control element and the housing. Some mounting mats and insulating elements (e.g., end cone insulation) include mostly inorganic fibres, with inorganic or organic binders, fillers and the like. Such mounting mats are commonly die cut, using metal blades, or laser cut out of larger sheets of inorganic fibre material.
Mounting mats such as the mats of the present disclosure are mostly cut out of a larger sheet of fibre material. It has been found that using a cutting blade or other such device to mechanically cut out mounting mats or insulation elements (e.g. end cone insulation) from such sheets of inorganic fibre material often results in the inorganic fibres being fractured or broken rather than actually cut. Because the fibres fracture, a substantial amount of fibre dust results from the mechanical cutting operation. The generation of dust from binder and/or filler materials may result as well. Such dust remains in the cut-out mats. Later, when the mounting mat or end cone insulation is incorporated into the pollution control device, dust escapes from the fibre material of the mat and can cause itching or skin irritation problems for the workers handling these mats. It is therefore desirable to reduce the amount of fibres and dust exiting the mat through its edge surfaces. The present disclosure is directed to reducing the amount of dust that escapes from such mats, especially while being handled during a pollution control device assembly operation.
Attempts to solve this problem have been made before. The international patent application WO 2006/055188 A1, for example, mentions inorganic fibre mounting and insulating sheet materials for use in pollution control devices with at least one edge of the inorganic fibre sheet material having at least one group of two or more fibres fused together.
Similarly, the U.S. Pat. No. 7,951,731 B2 addresses a problem of fibre scattering and, in one aspect, mentions an inorganic fibre mat including an inorganic fibre aggregated body which includes inorganic fibres, where at least a part of the inorganic fibres located on a surface of the inorganic fibre aggregate body is fused to each other by heat.